Compressors utilizing a refrigerant are used in refrigeration systems, such as refrigerators, car air conditioners, industrial refrigerators, and room air conditioners, and hydrofluorocarbon refrigerants (nonchlorine compounds, that is, hydrogen- and fluorine-containing hydrocarbons, free from chlorine, with at least a part of the hydrogen atoms substituted with fluorine; hereinafter referred to as "HFC refrigerants") have drawn attention as refrigerants for these refrigeration systems. R134a, R125, R32, R143a, and R152a, each consisting of a single compound, and R407C and R410A, each consisting of a mixture of those compounds, have been proposed as the HFC refrigerant. Regarding a base oil, for a refrigerator oil, used in combination with the hydrofluorocarbon refrigerant, a polyhydric alcohol ester compound is known to have excellent properties.
A refrigeration system comprises a refrigerating compressor, a condenser, an expansion mechanism (e.g., expansion valve, capillary tube and the like), an evaporator, etc., connected to one another in series. Various metal working oils are used for the production of components for these equipment and for assembling the system, and these metal working oils remain in the assembled refrigeration system. The metal working oils contain additives, for example, a sulfur extreme pressure agent, such as a disulfide, and a phosphorus extreme pressure agent, such as a phosphoric ester.